1. Field of the Invention
This invention relates in general to detecting objects by detecting light reflections from an object, and in particular to a system that detects polarization contrast between two polarizing angles.
2. Description of the Prior Art
This invention deals with a method and apparatus for detecting objects, such as military targets. The targets may be trucks, tanks, artillery, aircraft, command centers and other systems. The targets may be protected by camouflage, foliage, or may be painted with a camouflage paint.
U.S. Pat. No. 5,264,916, Nov. 23, 1993 and U.S. Pat. No. 5,345,308, Sep. 6, 1994 show systems for detection using polarization. In those systems, the field of view is alternately polarized between two angles of polarization which are orthogonal to each other. Man-made objects, particularly those which have specular or shiny surfaces, exhibit flashing as the light polarizes from the first angle to the second angle. This flashing indicates to the observer that a man-made object is present within the field of view.
Sometimes military hardware will be hidden in shadows, under camouflage within trees and under embankments or bridges. Objects within shadows are more difficult to detect because sunlight does not impinge directly on them and the polarization contrast is not as great.